Bombsight computer



March 23, 1948. s. DARLINGTON 2,438,112

' BOMBSIGHT COMPUTER Filed June 29, 1943 Sheets-Sheet 1 FIG. 2

' PHASE SHIFTER INVENTOR By 5. DARL/NGTON ATTORNEY March 23, 1948. s,|5ARL|NGT N 2,438,112

BOMBS IGHT COMPUTER Filed June 29, 1946 3 Sheets-Sheet 3 FIG. 6

' 5,:056) METER 15%;??? Has M E I D/F FERE N TM TOR 20 l2! 1" l -//a 2 R25 Ail S; H32

T ROTATED BY ROHTED BY MOTOR ll SUPPORT 23 FIG. 3 FIG 2 lNVENTOR 5.DARLING TON ATTORNEY Patented Mar. 23, 1948 omreo STATES PATENT OFFICE I2.435.112. nolvmsion'r ooMr'UrEit Sidney Darlington, New York, N; Y.,assignor Bell-Telephone Laboratories, Incorporated, New

york, I}, a corporation of New York A a Application June 29, 1943,serial No. 492,729

This invention. relates to a computer associated with an aerialbombsight; and particularly to a computer in which the data areexpressed in the form of electrical quantities.;

The object of the invention is a means for indicatingthat an aerialvehicle; is on the. course to beflown to-the point where a bomb may bereleased, and for indicating the distance togo to this spot, so that thebomb will fall on atarget.

A .feature of theginvention is a method and means forproducingeleotrical voltages/proportional to the horizontalirange andhorizontal deflection components ofwthe vector velocity of the aerialvehicle wit-h respectto thetarget.

Another featureofpthe-invention. is a means for producingelectricalvoltages proportional to the horizontal' range and deflectioncomponents of the total displacement or. the aerial vehicle from themoment of observation to the moment of impact. n e

Another feature of-the invention. is a means for comparing the ratio-of.the electrical Voltages proportional to the range and deflectioncomponents of the vector: velocities .of the aerial vehicle with the.ratio voiathe electrical voltages proportional tothe horizontal-rangeand deflection components of the totaldisplacement of the aerialvehiclefrom its predicted position at the instant of impact of. thebomb, whereby equamy of these ratios indicates the correct track to beflown. 1..

A further feature ofthe invention is-a means for deriving an electricalvoltage proportional to the horizontal range component time displacementof the vehicle,- and-another electrical voltage proportional to the"enangeain the" horizontal range' com onent thetirhe of fall of the bomb;and of comparing" these Voltages whereby equality of these voltagesindicates that the vehicle has reached the position" to release the beama .7

Th present computerrs assoc-med with a sight capable of continuouslymeasuring" an azimuth angle and a distance. r The azimuth angle ismeasured. i r'om. some convenient at the; aerial Vehicle, the head totail axis of an airplane, to the vertical. mane through theta'rget. Thedistahce is the slant distance from. the vehiole or airplane tothe'target. The loornbsight may be a simple optical instrument includinga theodollte' fo'r measunag the azimuth angle and an optical rangefinder for-measuring the distance, or a radio locating equipment capableofmeasuring the azimuth angle and slant distance. The range finder mayalso be used to measure the .6 Claims. (01. ass-61.5)

height .or elevation-.ofthe aerial vehicle above the surfaceof'thetearth. 'Th'emeasurement of height. andx-the continuousmeasurements of azimuth an le and: slant distance are supplied asvoltages to the computentogetherwith information in the form i'ofvoltages representing the ballistie characteristics (of the bombused',and the computer continuously indicates that the correct course is beingfio'wn, -and thatthe correct position has been attained to release thebomb to strike the target. I

The operation of the computer will be better understood from thedrawings in which:

Fig; 1 shows the geometrical relationships involved, projected on ahorizontal plane through the aerial vehicle;- p

Fig. 2 diagrammatically snows a radio locator equipment associated withthe, computer;

. Fig. 3 schematically shows a device for producing a rotationproportional to horizontal range;

Fig. 4 shows a thiiiiibni amplifier forming part of the device; I. i.

Fig. 5 schematically shows a device for producing a rotationproportional to the angle 6;

Fig. 6 schematically shows the computing e1ements of the invention.

As usual in aerial bombing technique, assume that the aerial vehicle isflying at constant speed and at constant height; At the commencement ofthe bombing run, the constant height of the aerial vehicle above theground is measured, say by the range finder. From this constant knownheight of the aerial vehicle, and the constantly measured slant distanceto the-target, the Computer continuously computes the horizontal rangefrom the aerial vehicle to the projection of the target. p

In Fig. -1, P represents the aerialvehicle such as an airplane headedalong the course PA. If a wind be blowing, the airplane willcontinuallydrift ofl the course and will actually travel along some track, such as1 3: 'Th'etai'get is located at O, and the computer is required tocontinuously indicate whether the vehicle is on the correct track PB,and whether the airplane has reached therelease point RP sothat a bombreleased at this position will fall on the target: 0;

If the airplane while steadily heading along the course PA at constantspeed and height, is driven by the wind to actually travel along thetrack PB, and, after releasing a bomb. at RP, continues at the samespeed along the trackPB, it will reach the point Eat the instant ofimpact of the bomb on the target. -.The distance OB; along the head totail axis of the airplane is known as the trail 3 T, and is tabulated inthe ballistic tables for the type of bomb used.

The angle APO between the course of the airplane and the vertical planethrough the target is designated 0. If the air structure be standard,the bomb will fall directly behind the airplane, in the plane of thehead to tail axis of the airplane, that is, the trail is in the line ofthe course, so that the angle BOC is equal to the angle APO which isequal to 0. Thus C, the range component of the trail equals T cos 9, andBC, the deflection component of the trail equals T sin 0. The distancePC'=R+T cos 0, may be termed the horizontal range component of the totaldisplacement from P to B of the airplane, and the distance T sin 0 thedeflection component of the total displacement with respect to point P.

The airplane is equipped with a gyroscopic device of known type, such asa device of the type shown in United States Patent 1,959,803, May 22,1934, B. A. Wittkuhns, which maintains an axis PX, having a fixeddirection in space, irrespective of the turning of the airplane. Theairplane has a ground speed along the track PB, repr'esentedby thevector PN. This vector PN may be resolved into two components PO, therange component of the ground speed and ON, the deflection component ofthe ground speed. The range component of the ground speed PO isevidently the rate of change in the horizontal range R, and, as therange is decreasing, this component is inherently negative and will bedesignated -R, where the dot indicates the time rate of change in thequantity. The deflection component ofthe ground speed ON is equal to R6,where 6 is the time rate of change in the angle 6. (This conversion ofvectors is shown, for example, on page 31, Alternating Currents andTransients, F. M. Colebrook, 1925, McGraw-Hill Book Company, 370 SeventhAvenue, New York.)

The angles PON and PCB are right angles making the triangles PON and PCBsimilar, thus which may be transformed into cos 0) %(sin 0) =0 (1) Theangle XPA, between the axis PX, having a fixed direction in space andthe course of the airplane PA, is indicated by the gyroscopic device andis designated A. The angle XPC, designated 6 is evidently equal to e-A.

If the airplane is heading along the course PA, and the track of theairplane is a straight line PB, then x will be constant, and 6:0. If theheading of the airplane changes, and 0 will both change at the samerate, so 6=0)\. Even if the airplane leaves the track PB and flies insome curved path, it may be shown that the relationship 6=a-7\ is stilltrue. Thus, for constant height, no matter what track is made good,Equation 1 is still valid, and indicates that the vehicle is on thecorrect track to pass through the correct release point for the bomb.

Let the vector PG represent the airspeed S, that is, the speed of theaerial vehicle relative to the air in the direction of the course. Letthe vector GN represent the wind velocity W relative to the ground,blowing from G to N at the angle 'y measured with respect to PO. DrawGit-normal to PC, and NZ normal to Gk. r

Then

-R=Pk0k= PkNl=S cos 0-W cos y Rb=Gk-Gz=s sin 0-W sin 7 When steering onthe correct track,

When the heading or track is not correct, this quantity will no longerbe zero, thus, let

In this expression, S, T, W and 'y are constant,

T W andare both less than unity, and are usually quite small. If thevehicle is at point P, and the only error is in the heading, then R willbe correct. Even if the vehicle is not on the correct track, the valueof R will be substantially unchanged. Thus, only the angle 6 dependsupon the instantaneous heading of the vehicle. It may be shown that Evaries substantially linearly with 0, when 0 has values from degrees to+90 degrees. Thus, a circuit designed to compute in accordance withEquation 1 will produce a voltage which in magnitude and polarity isalways proportional to the error in the heading of the vehicle.

If an electrical voltage, varying in proportion to Equation 1 beproduced, and supplied to a meter, the meter needle will be in thecenter of the scale when the airplane is on the correct track; when theairplane is to the right of the correct track, the needle will be to theleft of the center of the scale; when the airplane is to the left of thecorrect track, the needle will be to the right of the center of thescale, the meter thus indicating in which direction the airplane shouldbe turned in order to fly back on to the correct track.

The dotted lines in Fig. 1 show the condition as the airplane passesthrough the correct release point RP; The angle 0, between the courseand the range line has increased in magnitude causing a correspondingincrease in the angle 6, the angle A remaining unchanged. Afterreleasing a bomb at the point RP, the total displacement of the airplaneduring the time between the releasing of the bomb and its impact on thetarget will be the distance RPB. The horizontal range component of thistotal displacement is RPD, and this distance is evidently equal to thedistance RPO, which is the horizontal range R, plus the distance ODwhich is equal to T cos 0. The rate of change in the horizontal range isR., thus the total change in the horizontal range during the time offall of the bomb is evidently Rt, where t equals the time of fall of thebomb. The horizontal range component of the total displacement of theairplane during the time of fall of the bomb is evidently equal to thetotal increment in the horizontal range component during the same time,thus height H of the airplane, and thewiper I is continuously adjustedto have a displacement proportional to the slant range p. The voltageselected by the wiper 36 is approximately equal to the square of thehorizontal range. The voltage selected by the wiper I5 is of oppositepolarity to the voltages selected by the wipers 35 and 35. The voltagesselected by the wiper 55, which is equal to +H the voltage selected bythe wiper 36 which is approximately equal to +12. and the voltage fromthe wiper which is equal to -p are respectively supplied to a summingamplifier 51 which may be of the type shown in Fig. 4.

The winding of a relay 3! is connected in the output circuit of thesumming amplifier 31. The relay 38 is a polar relay, normally biased toa central position, andoperated in one direction or the other dependingupon the polarity of the voltage in the outputcircuit of the amplifier31. If the voltages summed up by the amplifier 31 are not equal to zero,the relay-38 will be operated in one direction or the other.

Current is supplied from a suitable source 39, through a 90-degree phaseshifting network 40 to one winding of a two-phase motor qL-which rotatesthe wiper 36,either directly or through suitable gearing, flexibleshafting .or other mechanism. Current may also be supplied from thesource 39 to the other winding of the motor 4!, the supply of current tothis winding and the phase of the current supplied being controlled bythe position of the armature of relay 38. Thus if the voltage in theoutput of the amplifier 31 is not equal to zero, the relay 38 will beoperated, starting the motor ll and rotating the wiper 36 in such adirection as to reduce the voltage in the output of the amplifier 31 tozero, releasing the relay 38. When the voltage in the output of theamplifier 31 is equal to zero, H +R p =0, and the displacement of theWiper 35 indicates the value of R, the horizontal range. Otherpotentiometers may be mounted so that their wipers will also be rotatedby the shaft of the motor 6!, an amount proportional to R, thehorizontal range.

The summing amplifier 31, shown in fi 3, may conveniently be of the typeshown in Fig. 4, including three thermionic amplifying devices 5B, 5!and 52 connected in cascade. The interstage coupling networks may be ofanyvtype suitable for the frequency range to be covered, thus, workingwithlow frequencies, the interstage coupling networks may convenientlybe, as shown, of the type disclosed in United States Patent 1,751,527,March 25, 1930, H. Nyquist. The amplifying devices 50', 51' and- 52 havebeen shown as simple triodes but, if higher voltage gain is desired,other known devices, such as suppressor grid pentodes, may be used. Theinput circuit of the triode 50 should be arranged so that in the absenceof 'an applied signal, the control grid is at ground potential.

' Current from a suitable source 53 is supplied through the couplingresistor 54 to the anodeof the output triode 52. In the absence of asignal applied to the amplifier, the anode current of the output triode52 is adjusted so that the voltage of the source 53 is wholly consumedin the resistor 54, thus the anode of the triode 52 is at groundpotential and no voltage is supplied to the output circuit. A source ofvoltage 55, having its negative pole connected to the cathode of theoutput triode 52 and its positive pole-connected to ground, maintainsthe anode current flowing in the triode 52.

-8 A large degree of negative or reverse feedback is supplied throughthe resistor 56 from the anode of the output triode 52 to the controlgrid of the first triode 50. The voltages selected by the wipers I5, 35and 36, Fig. 3, are respectively supplied through the resistors 51, 58and 59 to the control grid of the first triode 50. The efiect of thelarge degree of negative or reverse feedback supplied through theresistor 56 is to make the input impedance of the first triode 50 have avery low value, thus the movements of the wipers I5, 55 and 36 do notcause any interactions among the voltages selected. Another effect ofthe large degree of negative or reverse feedback is to make the voltageamplification of the complete amplifier, for any input, substantiallyindependent of the voltage amplification factors of the triodes 55, 5!and 52 and dependent almost entirely upon the ratio of the resistance ofthe feedback resistor 56 to the resistance of the resistor-in serieswith the particular source. Thus, when the summing repeater of Fig. 4 isused in connectionwith the system of Fig. 3, the input resistors 5?, 58and 59 should be made of equal value, and the resistance of the resistor55 adjusted with respect to the resistance of an input resistor so as togive the voltage gain necessary to secure correct operation of the relay38, Fig. 3.

If a negative voltage is applied to the control grid of the device 56,an amplified negative voltage will be applied to the control grid of thedevice 52, decreasing the anode current of the device 52, reducing thevoltage drop in the resistor 54 and causing a positive voltage to appearacross the output circuit. The amplifier shown in Fig. 4 thus reversesthe polarity of the voltage applied to the input circuit. If a pluralityof voltages be applied to the input circuit, the voltage across theoutput circuit will be'proportional to the sum of the appliedvolt-ages.If a voltage be applied through a capacitor 60 and resistor 6| in serialrelationship to the input circuit of the summing amplifier, the outputvoltage of the summing amplifier will contain a component proportionalto the derivative or time rate of change of the voltage applied throughthe capacitor 55.

Fig. 5 discloses a system similar to the system shown in Fig. 3 whichwill produce a rotation of a shaft proportional to the angle 6, Fig, 1.As aforesaid, the angle 6 is equal to the angle 0 minus the angle A. Avoltage source 88 of one polarity is connected to the potentiometerwinding 29 shown in Fig. 2. The wiper 30 of this potentiometer is movedby the tracking of the antenna structure through an angle proportionalto the azimuth angle 0. Another voltage source 88, of opposite polarityto the source 88 is connected across the windings of two otherpotentiometers 8i and 82. The wiper 83 is moved by the servomotorassociated with the gyroscopic device maintaining the axis PX, shown inFig. 1, through an angle proportional to the angle X. The voltagesselected by the wipers 30, 83 and 84 are respectively supplied throughthe input resistors of the summing amplifier 85 of the type shown inFig. 4. The voltage selectedby the wiper 83 is proportional to thevoltage selected by the wiper 3B is proportional to 49, and the voltageselected by the wiper 84 is approximately proportional to +(0 thus thevolt-ages supplied to the input of the summing amplifier 85 are equal to\0+(9- and should equal zero. If the sum of these voltages is not equalto zero, the relay 86 will be operated, starting the motor 81 whichrotates the wiper 84 until the sum of the voltages is in the center ofthe scale when the voltage applied to the summing amplifier H3 is zero,and to deflect to one side or the other of the center of the scale toindicate when the airplane is flying on one side or the other of thecorrect course.

A portion of the output voltage of the diiTeren tiator II 8 is suppliedthrough decoupling resistor I39 to the wiper of a potentiometer I3I, thewinding of potentiometer I3I being connected in parallel with thewinding of a second potentiometer I32. It is known that the time of fallit of a bomb is a function of the height of the airplane and of the airspeed of the airplane and the values of the time of fall for selectedvalues of the height and air speed of the airplane are tabulated in thefiring tables for the bomb to be used; The potentiometer winding I 3! isdesigned as described in column 6-to have a resistance varying inaccordance with the functional variations of the time of fall of thebomb with the height of the airplane, and the potentiometer winding I32is designed as described in column 6 to have a'resistance varying inaccordance with the functional variation of the time of fall of the bombwith the air speed of the plane. The wiper I33. is adjusted to themeasured height of the plane, and the wiper I34 is adjusted to themeasured air speed of the plane. The voltage selected by'the Wiper I34,which thus varies in accordance with Rt is supplied to an input resistorof the summing amplifier I35, which may be of the type shown in Fig. 4.

The voltage selected by the Wiper H6, proportional to R, is supplied bythe connection I36 to an individual input resistor f the summingamplifier I35.

The voltage from the source IilI is supplied through the decouplingresistor I 31 to the wiper of potentiometer I 38. The potentiometerwinding I38 is shunted by the variable rheostat I39, The wiper ofpotentiometer I38 is adjusted to the known height of the airplane, andthe wiper of the rheostat I3-9 is adjusted to the known air speed of theairplane, thus the potentiometer I38 and rheostat I39, like thepotentiometer I96 and rheostat I01, produce a voltage on the connectionI40 proportional to the trail T of the bomb. This voltage is applied toone diametrical point of a potentiometer winding MI having a resistanceper unit length varying in accordance with a sinusoidal function. Theother diametrical'point of the winding is grounded. The wiper I 42, likethe wipers III] and I23, is rotated by the support 23, Fig. 2, throughan angle 20, thus the voltage selected by the wiper I42 is proportionalto T cos 0, and this voltage is supplied through an individual inputresistor to the summing amplifier I35.

The output voltage of the summing amplifier I35 will thus beproportional to R+T cos fl-l-Rt, and this voltage will drop to zero whenthe correct point for releasing the bomb has been reached.

The output voltage of the summing amplifier I35 may be applied to ameter I 43, thus when the meter I43 falls to zero the bomb should bereleased. If desired, the meter I43 may be replaced by any suitableelectromechanical mechanism which will automatically release the bombwhen the current falls to zero.

If desired, the wipers of the potentiometers I96,

I-3I and I38 may be ganged to move together when setting in the measuredheight of the airplane, and similarly, the wipers of rheostats I31, I39and potentiometer I32 may be ganged to 12 move together when setting inthe measured airspeed of the airplane.

What is claimed is:

1. In a system for indicating that the correct track is being flown byan aerial vehicle so that a bomb dropped from said vehicle will land ona target, a grounded source of voltage, means connected to said sourceand controlled by observations of said target to fractionate the voltagefrom said source proportionally to the rate of change in the anglebetween a fixed direction and the vertical plane including saidvehicleand said target, a first potentiometer having a first wiper connected tosaid means and adjusted to select a voltage proportional to the trail ofsaid bomb, and a winding, means on said vehicle controlled byobservations of said target including a first shaft moved proportionallyto the horizontal range from said vehicle to said target and a secondshaft moved proportionally to the angle between the axis of said vehicleand said plane, a second potentiometer having a second wiper connectedto the winding of said first potentiometer and moved :by said secondshaft and a Winding varying in resistance with a sinusoidal functionconnected to ground, and a third potentiometer having'a windingconnected across the winding of said first potentiometer and a thirdWiper moved by said first shaft to select 2. voltage proportional tosaid rate of change multiplied by the ratio of said range to said trailplus the cosine of said latter angle.

2. In a system for indicating the point at which a bomb may be releasedfrom an aerial vehicle to strike a target, a source of voltage, firstmeans connected to said source and controlled byobservations of saidtarget to fractionate the voltage from said source proportionally to thehorizontal component of the. distance from said vehicle to said target,electronic means connected to said first means to produce a voltageproportional to the component of the ground speed of said vehicle in thedirection of said target, second means connected to said electronicmeans and adjusted to fractionate the voltage from said meansproportionately to the time of fall of said bomb, third means connectedto said source and adjusted to ifractionate the voltage from said sourceproportionately to the trail of said bom'b, fourth means connected tosaid third means and controlled by observations of said target tofurther fractionate the voltage from said source proportionally to thecosine of the azimuthal angle between the course of said vehicle and thevertical plane through said vehicle and said target, a feedbackamplifier having an input circuit connected to said first, second andfourth means to add the voltages from said means, and an output circuit,and a meter connected to said output circuit to indicate the sum of saidvoltages. V

3. In ,a system for indicating the point at which a bomb may be releasedfrom an aerial vehicle to strike a target, a source of voltage, firstmeans connected to said source and controlled by observations of saidtarget to fractionate said voltage proportionally to thehorizontal'range from said vehicle to said target, second, meansconnected'to said source'and controlled by observations of said targetto fractionate said voltage proportionally to the horizontal rangecomponent of the trail of said bomb, difierentiating means connected tosaid first meansto produce a voltage proportional to the time rate ofchange of said first fractionated voltage, the third means connected tosaid differentiating means and adjusted to fractionate the voltagefromisaid means proportionately toth e; time of fall of said bomb,electronic means having an input circuit connected te said first,-seeondand thirdmeans to add the voltages from said means, andalnoutputcircuit, and a meter connected to said output circuit toindicate when the sum of said voltages. falls tozero.

4. In a system for indicating the course to be flown by a bomber to dropa bomb on a target, mechanism controlled in accordance with observationsof the target to rotate a first shaft proportionally to the azimuthangle of the target and a second shaft proportionally to the horizontalrange to the target, first means controlled by said first shaft to formthe source of a first voltage proportional to the angular velocity ofsaid shaft, second means controlled by said second shaft to form thesource of a second voltage proportional to the rate of change ofhorizontal range, first potentiometer means connected to the source ofsaid first voltage and adjusted to fractionate said voltage inverselyproportionally to the trail of said bomb, second potentiometer meansconnected to said first potentiometer means and controlled by saidsecond shaft to further fractionate said voltage proportionally to thehorizontal range, third potentiometer means connected 'to the source ofsaid first voltage and controlled by said first shaft to fractionatesaid voltage proportionally to the cosine of said azimuth angle, fourthpotentiometer means connected to the source of said second voltage andcontrolled by said second shaft to fractionate said voltage inverselyproportionally to said range, fifth potentiometer means connected tosaid fourth potentiometer means and controlled by said first shaft tofurther fractionate said latter voltage proportionally to the sine ofsaid azimuth angle, and means connected to said second, third and fifthpotentiometer means to oppose the voltages from the second and thirdmeans to the voltage from the fifth means and indicate the difference,whereby said indication varies in direction and magnitude with the senseand extent of the deviation of the course of the bomber from the correctcourse.

5. In a system for indicating the course to be flown by a bomber to dropa bomb on a target, mechanism controlled in accordance with observationsof the target to rotate a first shaft proportionally to the anglebetween an axis fixed in direction and the vertical plane containing thebomber and the target, to rotate a second shaft proportionally to theangle between the axis of the bomber and said plane, and to rotate athird shaft proportionally to the horizontal range to the target, firstmeans controlled by said first shaft to form the source of a firstvoltage proportional to the angular velocity of said shaft, second meansconnected to the source of said first voltage and adjusted tofractionate said voltage inversely proportionally to the trail of thebomb, third means connected to said second means and controlled by saidthird shaft to further fractionate said voltage proportionally to thehorizontal range, fourth means connected to the source of said firstvoltage and controlled by said second shaft to fractionate the firstvoltage proportion ally to the cosine of the angle of rotation of saidshaft, fifth means controlled by said third shaft to form the source ofa second voltage proportional to the angular velocity of said thirdshaft, sixth means connected to the source of said sec- 14 0nd voltageand controlled by said third shaft to fractionate said secondvoltageinversely proportionally to the horizontal" range, seventh meansconnected to said sixth; means and controlled by said second-shaftto;fractionate the voltage opornoaanytotnsme5r the angle of rotation ofsaid second shaft; and meter ineans connected" to said third, fourth andseventh means to oppose the voltages from said third and fourth means tothe voltage from said seventh means and indicate the difference, wherebysaid indication varies in direction and magnitude with the sense andextent of the deviation of the course of the bomber from the correctcourse.

6. In a system for indicating the course to be fioWn by a bomber and thedistance to go to drop a bomb on a target, mechanism controlled inaccordance with observations of the target to r0- tate a first shaftproportionally to the angle between an axis fixed in direction and thevertical plane containing the bomber and target, to rotate a secondshaft proportionally to the angle between the axis of the bomber andsaid plane, and to rotate a third shaft proportionally to the horizontalrange to the target, means controlled by said first shaft to form thesource of a first voltage proportional to the angular velocity of thefirst shaft, means controlled by said third shaft to form the source ofa second voltage proportional to the displacement of the third shaft andthe source of a third voltage proportional to the angular velocity ofthe third shaft, first potentiometer means connected to the source ofsaid first voltage and adjusted to select a voltage inverselyproportional to the trail of the bomb,

second potentiometer means connected to said first potentiometer meansand controlled by said third shaft to select a voltage proportional tothe horizontal range, third potentiometer means connected to the sourceof said first voltage and controlled by said second shaft to select avoltage proportional to the cosine of the angle of rotation of thesecond shaft, fourth potentiometer means connected to the source of saidthird voltage and controlled by said third shaft to select a voltageinversely proportional to the horizontal range, fifth potentiometermeans connected to said fourth means and controlled by said second shaftto select a voltage proportional to the sine of the angle of rotation ofsaid second shaft, first meter means connected to said second, third andfifth potentiometer means to 0D- pose the voltages from the second andthird means to the voltage from the fifth means and indicate thedifference, whereby said indication varies in direction and magnitudewith the sense and extent of the deviation of the course of the bomberfrom the correct course, sixth potentiometer means connected to thesource of said third voltage and adjusted to select a voltageproportional to the time of fall of the bomb, a source of a fourthvoltage adjusted to be proportional to the trail of the bomb, seventhpotentiometer means connected to the source of the fourth voltage andcontrolled by the second shaft to select a voltage proportional to thecosine of the angle of rotation of the second shaft and second metermeans connected to said sixth and seventh means and the source of saidsecond voltage to oppose the voltage of said sixth means to the othervoltages and indicate the difference, whereby said indication isproportional to the distance to go to the correct spot to drop the bomb.

SIDNEY DARLINGTON.

(References on following page) UNITED STATES PATENTS Number Name DateInglis Jan, 11, 1938 Chafee et a1 June 20, 1939 Number m'e Dafi BaroniSept. 29, 1942 Schneider June 16, 1925 Wey Nov. 1, 1938 Methlin May 11,1936 Williams Apr. 5, 1938 Martin Juner3, 1941 Parkinson Sept. 10, 1946

